OBJECTIVE: Vitamin A and related compounds (retinoids) have been shown to have preventive and therapeutic effects on several types of tumors in the intact animal, to prevent carcinogen-induced hyperplasia in organ culture, and to restore some functions of normalcy to transformed cells in culture. Vitamin A deficient animals are also more susceptible to carcinogens and more prone to development of spontaneous tumors. The overall objective is to study the anti-tumor effects of retinoids. Specifically, the proposal is to study the effects of retinoids on tumor cells in cultures; a. to develop an in vitro model for the study of the direct effects of retinoids on tumor cell proliferation, b. to study direct effects of retinoids on parameters of transformation, c. to resolve the discrepancy of results of retinoid treatment on tumors grown in vitro and in the animal, and d. to study the mechanism of action of retinoids on DNA synthesis and control of proliferation of tumor cells.